It has previously been proposed to make substrates for printed circuits and to then apply circuit tracks on the substrate, for example by printing, such as screen printing, and then firing the printed material on the substrate. The printed material may be either highly conductive, thus forming a printed conductor, or may be in the form of resistor layers, or dielectric layers. The material is usually applied in the form of a paste, and the substrate may be made of a ceramic, typically aluminum oxide. Enameled steel is also used in some applications.
Substrates made of enameled steel have various advantages over those of ceramic. Enameled steel substrates, up to now, have been used only for special applications. One of the reasons is the low softening temperature of the enamel which limits the firing temperatures of the respective pastes to below about 650.degree. C.